The present invention relates to an aluminum line formed as a film on a semiconductor substrate and a method of forming the same.
Stress migration is known as a phenomenon which causes the breaking of the aluminum line and the occurrence of a void. Electromigration is also known as a phenomenon which causes the breaking of the aluminum line.
The achieving of high integration and high speed in semiconductor integrated circuits has recently become highly desirable. High integration and high speed require the use of specialized techniques for microminiaturization and multi-metal-layer lamination in a line structure. Microminiaturization of the line structure necessitates the design of the aluminum line of much narrower width than has previously been attained. Each aluminum line of the multi-metal-layer line structure has its narrowest part at a point where its rank (which layer it is in) changes or at a through hole, resulting in a reduction of its sectional area. However, a reduction of the sectional area of the line causes an increased current density which leads to the phenomena-known as electromigration, which shortens an aluminum line's life. A FIG. 9 shows the relationship between the width of the aluminum line and the electromigration life of a device made using an Al-Si line formed by an S-Gun apparatus. The relationship shown in FIG. 9 is an experimental result at 150.degree. C. when a current of 16 mA is supplied to the Al-Si line whose thickness is 0.9 .mu.m. Usually, the width of a line is about 4 .mu.m and the line's life is about 10.sup.3 hours. A device which can have practical use is almost impossible if the width of an line is narrower than 2 .mu.m, since an increased current density makes the line's life about 10.sup.2 hours. Hence, in order to suppress electromigration, copper or titanium have been added to an Al-Si alloy line, thus providing an Al-Si-Cu alloy line or Al-Si-Ti alloy line respectively.
However, while those aluminum alloy lines can suppress electromigration to a certain degree, they can not suppress it beyond this certain degree.